41 Logic Puzzles And Brainteasers That Will Probably Challenge Your Mind
Logic puzzles can be an actual work of art. It just takes a few simple elements put together in the right way to create a brainteaser that will entertain friends and families for hours. Not only do they test your wits, but they also make you think about things in a completely different way. And the best thing about mind puzzles is that you don’t need to be a smartass to solve them. Putting your brain to work is enough! You may need to use clues given in the questions and really focus on what these brain puzzles are asking you to do.
Today we want to challenge you with some of the most fantastic logic riddles we found scattered on the internet, including some that will really challenge your brain and force you to think outside the box. The answers to these logic problems often aren’t easy to come up with, but if you use your brain properly, there’s a good chance you’ll figure them out before too long! So let’s get started!
#1A man is caught on the king's property. He is brought before the king to be punished. The king says, "You must give me a statement. If it is true, you will be killed by lions. If it is false, you will be stomped by trampling of wild buffalo. If I can’t figure it out, I’ll have to let you go.” Sure enough, the man was released. What was the man's statement?
Answer: "I will be stomped by trampling of wild buffalo.” This stumped the king because if it’s true, he’ll be killed by lions, which would render the statement not true. If it’s a lie, he’d be killed by wild buffalo, which would make it a truth. Since the king had no solution, he had to let the man go.
#2There are two ducks in front of a duck, two ducks behind a duck and a duck in the middle. How many ducks are there?
Answer: Three. Two ducks are in front of the last duck; the first duck has two ducks behind; one duck is between the other two.
#3Two fathers took their sons fishing. Each man and son caught one fish, but when they returned to camp there were only 3 fish. How could this be? (None of the fish were eaten, lost, or thrown back)
Answer: There were only three people. The son, his father, and his grandfather.
#4You are about to leave for holiday, but you forgot socks!
You race back to your room, but the power is off so you can't see sock colors.
Never mind, because you remember that in your drawer there are ten pairs of green socks, ten pairs of black socks, and eleven pairs of blue socks, but they are all mixed up.
How many of your socks do you need to take before you can be sure to have at least one matching pair?
Answer: Four. Although there are many socks in the drawer, there are only three colors, so if you take four socks then you are guaranteed to have at least one matching pair.
#5A farmer wants to cross a river and take with him a wolf, a goat and a cabbage. He has a boat, but it can only fit himself plus either the wolf, the goat or the cabbage. If the wolf and the goat are alone on one shore, the wolf will eat the goat. If the goat and the cabbage are alone on the shore, the goat will eat the cabbage. How can the farmer bring the wolf, the goat and the cabbage across the river without anything being eaten?
Answer: First, the farmer takes the goat across. The farmer returns alone and then takes the wolf across, but returns with the goat. Then the farmer takes the cabbage across, leaving it with the wolf and returning alone to get the goat.
#6There are only two barbers in town. One of them has a nice, neatly trimmed head of hair. The other one's hair is a complete mess. Which of the two barbers should you go to and why?
Answer: The one with messy hair, as they cut the neat barber's hair.
#7You’re at a fork in the road in which one direction leads to the City of Lies (where everyone always lies) and the other to the City of Truth (where everyone always tells the truth). There’s a person at the fork who lives in one of the cities, but you’re not sure which one. What question could you ask the person to find out which road leads to the City of Truth?
Answer: “Which direction do you live?” Someone from the City of Lies will lie and point to the City of Truth; someone from the City of Truth would tell the truth and also point to the City of Truth.
#8You have two ropes that each take an hour to burn, but burn at inconsistent rates. How can you measure 45 minutes? (You can light one or both ropes at one or both ends at the same time.)
Answer: Because they both burn inconsistently, you can’t just light one end of a rope and wait until it’s 75 percent of the way through. But, this is what you can do: Light the first rope at both ends, and light the other rope at one end, all at the same time. The first rope will take 30 minutes to burn (even if one side burns faster than the other, it still takes 30 minutes). The moment the first rope goes out, light the other end of the second rope. Because the time elapsed of the second rope burning was 30 minutes, the remaining rope will also take 30 minutes; lighting it from both ends will cut that in half to 15 minutes, giving you 45 minutes all together.
#9The day before two days after the day before tomorrow is Saturday. What day is it today?
Answer: Friday. The “day before tomorrow” is today; “the day before two days after” is really one day after. So if “one day after today is Saturday,” then it must be Friday.
#10Abigail, Oliver, Rosa, and Blake all attend the same summer camp, where they can cook, kayak, rock climb, and zip-line. Each child has a different favorite activity. Abigail’s favorite activity isn’t rock climbing. Oliver is afraid of heights. Rosa can’t do her favorite activity without a harness. Blake likes to keep his feet on the ground at all times. Can you figure out who likes what?
Answer: Abigail likes to zip-line, Oliver likes to kayak, Rosa likes to rock climb, and Blake likes to cook.
#11There is a lightbulb inside a closet. The door is closed, and you cannot see if the light is on or off through the door. However, you know the light is off to start. Outside of the closet, there are three light switches. One of the switches controls the lightbulb in the closet. You can flip the switches however you want, but once you open the door, you can no longer touch the switches. How do you figure out without a doubt which switch controls the light?
Answer: Flip switch number 1 and wait a few minutes. Flip switch number 1 back to its original position, and then immediately flip switch number 2.
Open the door. If the light is on, then switch number 2 controls it. If the light is off, then go and feel the bulb with your hand. If the bulb is hot, the switch number 1 controls it, and if the bulb is cold, then switch number 3, the one you did not touch, controls it.
#12There is a barrel with no lid and some wine in it. “This barrel of wine is more than half full,” says the woman. “No, it's not,” says the man. “It’s less than half full.” Without any measuring implements and without removing any wine from the barrel, how can they easily determine who is correct?
Answer: Tilt the barrel until the wine barely touches the lip of the barrel. If the bottom of the barrel is visible then it is less than half full. If the barrel bottom is still completely covered by the wine, then it is more than half full.
#13Four playing cards, one of each suit, lie face down on a table. They are a three, a four, a five, and a six. The cards on either side of the four are black.
The club is to the right of the three but not next to it. The spade is to the left of the heart. The middle two cards add up to an even number. Neither of them is a club. Can you determine the cards’ suits and their order?
Answer: From left to right: Three of diamonds, six of spades, four of hearts, five of clubs.
#14Five friends (Allegra, Ben, Clara, Flora, and Zach) are each allergic to something different: pollen, shellfish, bee stings, cats, or nuts. Allegra has a food allergy. Ben can play with his kitten for hours without issue (or medicine). Clara’s allergy is not related to animals. Flora has seasonal allergies. Can you figure out who is allergic to what?
Answer: Allegra is allergic to shellfish, Ben to bee stings, Clara to nuts, Flora to pollen, and Zach to cats.
#15If five cats can catch five mice in five minutes, how long will it take one cat to catch one mouse?
Answer: Five minutes. Using the information we know, it would take one cat 25 minutes to catch all five mice (5x5=25). Then working backward and dividing 25 by five, we get five minutes for one cat to catch each mouse.
#16Four people are crossing a bridge at night, so they all need a torch—but they just have one that only lasts 15 minutes. Alice can cross in one minute, Ben in two minutes, Cindy in five minutes and Don in eight minutes. No more than two people can cross at a time; and when two cross, they have to go at the slower person’s pace. How do they get across in 15 minutes?
Answer: Alice and Ben cross first in two minutes, and Alice crosses back alone with the torch in one minute. Then the two slowest people, Cindy and Don, cross in eight minutes. Ben returns in two minutes, and Alice and Ben return in two minutes. They just made it in 15 minutes exactly.
#17A girl meets a lion and unicorn in the forest. The lion lies every Monday, Tuesday and Wednesday and the other days he speaks the truth. The unicorn lies on Thursdays, Fridays and Saturdays, and the other days of the week he speaks the truth. “Yesterday I was lying,” the lion told the girl. “So was I,” said the unicorn. What day is it?
Answer: Thursday. The only day they both tell the truth is Sunday; but today can’t be Sunday because the lion also tells the truth on Saturday (yesterday). Going day by day, the only day one of them is lying and one of them is telling the truth with those two statements is Thursday.
#18A person bought an item for $7, sold it for $8, bought it back for $9, and sold it for $10. How much profit did he make?
Answer: He made $2.
#19There are five gears connected in a row, the first one is connected to the second one, the second one is connected to the third one, and so on.
If the first gear is rotating clockwise what direction is the fifth gear turning?
#20Each of five neighborhood dogs (Saber, Ginger, Nutmeg, Pepper, and Bear) is enjoying one of the following activities: getting its ears scratched, playing catch, taking a nap, burying a chew toy, and going for a walk. Pepper is either playing catch or burying a chew toy. Neither Ginger nor Saber nor Bear is on a walk. One of the dogs named after a spice is getting its ears scratched. A dog not named for a spice is playing catch. Bear is getting some exercise.
Can you figure out what each pooch is doing?
Answer: Saber is taking a nap, Ginger is getting her ears scratched, Nutmeg is going for a walk, Pepper is burying a chew toy, and Bear is playing catch.
#21Six neighborhood children (Leisha, Benito, Delia, Charlotte, Weldon, and Zina) were measured yesterday. Weldon is taller than Delia but shorter than Zina. Leisha is taller than Benito but shorter than Delia and Weldon. Benito is not the shortest. Can you put them in order of height from tallest to shortest?
Answer: Zina, Weldon, Delia, Leisha, Benito, Charlotte.
#22Susan and Lisa decided to play tennis against each other. They bet $1 on each game they played. Susan won three bets and Lisa won $5. How many games did they play?
Answer: Eleven. Because Lisa lost three games to Susan, she had lost $3 ($1 per game). So, she had to win back that $3 with three more games, then win another five games to win $5.
#23A bad guy is playing Russian roulette with a six-shooter revolver. He puts in one bullet, spins the chambers and fires at you, but no bullet comes out. He gives you the choice of whether or not he should spin the chambers again before firing a second time. Should he spin again?
Answer: Yes. Before he spins, there’s a one in six chance of a bullet being fired. After he spins, one of those chances has been taken away, leaving a one in five chance and making it more likely a bullet will be fired. Best to spin again.
#24Daniel, Emily, Marciano, and Christina are all wearing solid-colored shirts. Their shirts are red, yellow, green, and blue. Only the person wearing blue tells the truth, while the other three lie. They make the following statements:
Daniel: “Marciano is wearing red.”
Emily: “Daniel is not wearing yellow.”
Marciano: “Emily is wearing blue.”
Christina: “I will wear blue tomorrow.”
Can you determine each person’s shirt color, and whether we can expect to see Christina in blue tomorrow?
Answer: Daniel is wearing yellow, Emily is in red, Marciano is in green, and Christina is in blue. Christina will wear a blue shirt again tomorrow.
#25Jack is looking at Anne. Anne is looking at George. Jack is married, George is not, and we don’t know if Anne is married. Is a married person looking at an unmarried person?
Answer: Yes. If Anne is married, then she is married and looking at George, who is unmarried. If Anne is unmarried, then Jack, who is married, is looking at her. Either way, the statement is correct.
#26Ruby and Lewis are expecting… Triplets! They already know what they will name their three children, but they aren’t sharing the names until the babies are born. For now, this is all they’ll say:
· All three babies are boys.
· Their names are six letters long and anagrams of one another.
· Their names include both of their parents’ initials, but none of the other letters in their parents’ first names.
What will Ruby and Lewis name their triplets?
Answer: Arnold, Roland, and Ronald.
#27A joint Father’s Day and graduation party is being thrown for Michael, Ken, James, Alberto, Elias, and Stephanie. Three of them are newly minted high school graduates. The other three are their dads. Stephanie went to the senior prom with Michael’s son. Elias and James played on the school’s baseball team. One of them is Alberto’s son. Michael and Elias are not related. Can you match the high school graduates to their fathers at this joint celebration?
Answer: Alberto is Elias’ dad, Ken is Stephanie’s dad, and Michael is James’ dad.
#28There are three crates, one with apples, one with oranges, and one with both apples and oranges mixed. Each crate is closed and labeled with one of three labels: Apples, Oranges, or Apples and Oranges. The label maker broke and labeled all of the crates incorrectly. How could you pick just one fruit from one crate to figure out what’s in each crate?
Answer: Pick a fruit from the crate marked Apples and Oranges. If that fruit is an apple, you know that the crate should be labeled Apples because all of the labels are incorrect as they are. Therefore, you know the crate marked Apples must be Oranges (if it were labeled Apples and Oranges, the Oranges crate would be labeled correctly, and we know it isn’t), and the one marked Oranges is Apples and Oranges. Alternately, if you picked an orange from the crate marked Apples and Oranges, you know that crate should be marked Oranges, the one marked Oranges must be Apples, and the one marked Apples must be Apples and Oranges.
#29Three men are lined up behind each other. The tallest man is in the back and can see the heads of the two in front of him; the middle man can see the one man in front of him; the man in front can’t see anyone. They are blindfolded and hats are placed on their heads, picked from three black hats and two white hats. The extra two hats are hidden and the blindfolds removed. The tallest man is asked if he knows what color hat he’s wearing; he doesn’t. The middle man is asked if he knows; he doesn’t. But the man in front, who can’t see anyone, says he knows. How does he know, and what color hat is he wearing?
Answer: Black. The man in front knew he and the middle man aren’t both wearing white hats or the man in the back would have known he had a black hat (since there are only two white hats). The man in front also knows the middle man didn’t see him with a white hat because if he did, based on the tallest man’s answer, the middle man would have known he himself was wearing a black hat. So, the man in front knows his hat must be black.
#30The Reds, the Grays, the Blues, and the Blacks have a round-robin tournament. Each team plays each other team once, for a total of six games.
The Blacks won more games than the Blues. The Grays lost more games than the Blues. The Reds tied the Blacks (this was the only tie in the tournament). Who won the game between the Reds and the Blues?
Answer: The Reds.
#31At the Pet Show recently I noticed that all except two of the entries were cats, all except two were dogs, and all except two were fish. How many of each animal were at the Pet Show?
Answer: All except two were dogs and all except two were cats. So two animals were not dogs and two animals were not cats. One of the "not dogs" could have been a cat, and one of the "not cats" could have been a dog. Combine this with the fact that all except two of the pets were fish and we have the result: one dog, one cat, one fish - three animals at the Pet Show.
#32A teacher writes six words on a board: “cat dog has max dim tag.” She gives three students, Albert, Bernard and Cheryl each a piece of paper with one letter from one of the words. Then she asks, “Albert, do you know the word?” Albert immediately replies yes. She asks, “Bernard, do you know the word?” He thinks for a moment and replies yes. Then she asks Cheryl the same question. She thinks and then replies yes. What is the word?
Answer: Dog. Albert knows right away because he has one of the unique letters that only appear once in all the words: c o h s x i. So, we know the word is not “tag.” All of these unique letters appear in different words, except for “h” and “s” in “has,” and Bernard can figure out what the word is from the unique letters that are left: t, g, h, s. This eliminates “max” and “dim.” Cheryl can then narrow it down the same way. Because there is only one unique letter left, the letter “d,” the word must be “dog.”
#33A man has 53 socks in his drawer: 21 identical blue, 15 identical black and 17 identical red. The lights are out and he is completely in the dark. How many socks must he take out to make 100 percent certain he has at least one pair of black socks?
Answer: 40 socks. If he takes out 38 socks (adding the two biggest amounts, 21 and 17), although it is very unlikely, it is possible they could all be blue and red. To make 100 percent certain that he also has a pair of black socks he must take out a further two socks.
#34Five people were eating apples, A finished before B, but behind C. D finished before E, but behind B. What was the finishing order?
Answer: CABDE. Putting the first three in order, A finished in front of B but behind C, so CAB. Then, we know D finished before B, so CABD. We know E finished after D, so CABDE.
#35You have five boxes in a row numbered 1 to 5, in which a cat is hiding. Every night he jumps to an adjacent box, and every morning you have one chance to open a box to find him. How do you win this game of hide and seek?
Answer: Check boxes 2, 3, and 4 in order until you find him. Here’s why: He’s either in an odd or even-numbered box. If he’s in an even box (box 2 or 4) and you check box 2 and here’s there, great; if not you know he was in box 4, which means the next night he will move to box 3 or 5. The next morning, check box 3; if he’s not there that means he was in box 5 and so the next night he’ll be in box 4, and you’ve got him. If he was in an odd-numbered box to begin with (1, 3, or 5), though, you might not find him in that first round of checking boxes 2, 3 and 4. But if this is the case, you know that on the fourth night he’ll have to be in an even-numbered box (because he switches every night: odd, even, odd, even), so then you can start the process again as described above. This means if you check boxes 2, 3, and 4 in that order, you will find him within two rounds (one round of 2, 3, 4; followed by another round of 2, 3, 4).
#36Let’s pretend we’re on the metric system and use kilograms instead of pounds to give us a starting base number of 100. Four people (Alex, Brook, Chris and Dusty) want to cross a river in a boat that can only carry 100kg. Alex weighs 90kg, Brook weighs 80kg, Chris weighs 60kg and Dusty weighs 40kg, and they have 20kg of supplies. How do they get across?
Answer: There may be a couple variations that will work, but here’s one way: Chris and Dusty row across (combined 100kg), Dusty returns. Alex rows over, and Chris returns. Chris and Dusty row across again, Dusty returns. Brook rows across with the supplies (combined 100kg), and Chris returns. Chris and Dusty row across again.
#37Suppose there is this little town with a finite numer of people:
· No two inhabitants have exactly the same number of hairs.
· No inhabitant has exactly 409 hairs.
· There are more inhabitants than there are hairs on the head of any inhabitant.
So, what is the largest possible number of inhabitants in that little town?
#38George, William, John, Abe, and Millard have their birthdays on consecutive days, all between Monday and Friday. George’s birthday is as many days before Millard’s and William’s is after Abe’s. John is two days older than Abe. Millard’s birthday is on Thursday. Can you figure out whose birthday is on each day?
Answer: John’s is on Monday, George’s on Tuesday, Abe’s on Wednesday, Millard’s on Thursday, and William’s on Friday.
#39There are three bags, each containing two marbles. Bag A contains two white marbles, Bag B contains two black marbles, and Bag C contains one white marble and one black marble. You pick a random bag and take out one marble, which is white. What is the probability that the remaining marble from the same bag is also white?
Answer: 2 out of 3. You know you don’t have Bag B. But because Bag A has two white marbles, you could have picked either marble; if you think of it as four marbles in total from Bags A and C, three white and one black, you’ll have a greater chance of picking another white marble.
#40There are three people (Alex, Ben and Cody), one of whom is a knight, one a knave, and one a spy. The knight always tells the truth, the knave always lies, and the spy can either lie or tell the truth. Alex says: "Cody is a knave.” Ben says: "Alex is a knight.” Cody says: "I am the spy.” Who is the knight, who the knave, and who the spy?
Answer: We know Ben isn’t telling the truth because if he was, there would be two knights; so Ben could be either the knave or the spy. Cody also can’t be the knight, because then his statement would be a lie. So that must mean Alex is the knight. Ben, therefore, must be the spy, since the spy sometimes tells the truth; leaving Cody as the knave.
#41You are given three doors to choose from, one of which contains a car and the other two contain goats. After you’ve chosen one but haven’t opened it, Monty, who knows where everything is, reveals the location of a goat from behind one of the other two doors. Should you stick with your original choice or switch, if you want the car?
Answer: You should switch. At the beginning, your choice starts out as a one in three chance of picking the car; the two doors with goats contain 2/3 of the chance. But since Monty knows and shows you where one of the goats is, that 2/3 chance now rests solely with the third door (your choice retains its original 1/3 chance; you were more likely to pick a goat to begin with). So, the odds are better if you switch.